Saturday, July 21, 2007

Martian Dust Storms Engulf Planet - space.com

posted: 20 July 200708:17 am ETUpdated at 12:03 pm EasternEditor's Note: In a newer story, NASA officials discuss the possibility of the end to the rover mission.

The surface of Mars is now obscured by a globe-engulfing veil of dust, posing a potentially longer-lasting threat to NASA's twin surface rovers.

Massive regional storms have been whipping up dust on the red planet since late June. Now, they've combined to create a "planet-encircling veil of dust," according to a statement from Malin Space Science Systems (MSSS), which operates a camera on the Mars Reconnaissance Orbiter for NASA.

"The dust raised by these individual storms has obscured most of the planet over the past few weeks," the release stated.

A series of images shows how the regional storms, which covered about 10 million square miles (25.9 million square kilometers) two weeks ago, have lifted enough dust to blot out the surface of the red planet.

Sun-obscured explorers

The Mars rovers Spirit and Opportunity weathered the regional storms by cutting back their activity, but the global dust event may escalate danger to the rovers that depend on sunlight to survive the bone-chilling cold of the planet.

Steve Squyres of Cornell University, who is the lead scientist of the Mars Exploration Rover Project, said earlier this week that the dust levels are some of the worst the rover team has seen.

"To give you a sense of the 'thickness' of the dust, the brightness of the sun as viewed from the surface is now down to less than 5 percent of what it would be with a perfectly transparent atmosphere," Squyres told SPACE.com. "Of course, Mars never has a perfectly transparent atmosphere, but the sun is still very faint."

The saving grace for the rovers, however, is that the dust creates a glow of indirect sunlight. The effect is similar to Earth's cloudy weather, which blocks the sun but does not completely prevent light from reaching the ground.

"Even if it's cloudy enough that the sun is obscured completely, it's not pitch black out," Squyres said. "The sunlight gets scattered through the clouds. Same thing with the dust clouds on Mars."Sleeping it out

Despite the trickle of sunlight, the thick haze of red dust is gobbling up most of the rovers' solar power, Squyres said. As of Monday Spirit and Opportunity were "both actively doing science" near their respective sites at Gusev Crater and Meridiani Planum, but are now in an energy-conserving "sleep" mode.

"Rather than doing science, we're focused right now on conserving power and waiting for conditions to improve," Squyres said. If the rovers expend too much energy, they may be unable to warm their electronics and prevent circuit-snapping temperatures.

"One side benefit of the high winds that have caused this dust storm is that they have done a wonderful job of removing dust from the solar arrays on both rovers," he said, going so far as to say that Opportunity's solar panels are cleaner than they were just months after landing in 2004.

Still, Squyres noted that energy collected by the rovers' solar panels is about one-third of the level the first generated, so their activity is limited-and may be limited for months.

Mars mission specialists have said the storms, first reported by SPACE.com, could become the worst since Mars was entirely enshrouded by dust in January of 2001. But the science of predicting martian weather is in its infancy, so uncertainty has been the only constant these past several weeks.

"As with previous large dust-raising events on Mars, once the active storms die down, many weeks to months will pass before the dust settles out and the atmosphere clears," the Malin scientists said in their latest assessment.

Sunday, July 01, 2007

Nasa readies for asteroid mission - space.com

A Nasa spacecraft set for launch early next month will explore the two biggest asteroids in the Solar System.

Asteroids are believed to be the building blocks of planets - primordial relics left over from the formation of the Solar System 4.6 billion years ago.

The Dawn mission will launch from Cape Canaveral Air Force Station, Florida on 7 July, on a mission to study the asteroids Ceres and Vesta.

Dawn will reach Vesta in 2011 before going on to visit Ceres in 2015.

We're going back in time to the early Solar System

Christopher Russell, UCLA

"Ceres and Vesta have been altered much less than other bodies," said Christopher Russell, the Dawn mission's chief scientist.

"The Earth is changing all the time; the Earth hides its history, but we believe that Ceres and Vesta, formed more than 4.6 billion years ago, have preserved their early record."

CERES

Biggest object in the asteroid belt

930km (580 miles) across

Discovered in 1801 by Giuseppe Piazzi

Icy layer beneath dusty surface

Ceres is almost spherical and is thought to harbour a layer of water ice some 60 to 120km (40 to 80 miles) thick beneath its rocky surface.

At a meeting of the International Astronomical Union (IAU) last year, Ceres was elevated in status from merely the biggest body in the asteroid belt, to a "dwarf planet" - the same designation now held by Pluto.

While Ceres is a "wet" object, Vesta is devoid of water and appears to have been resurfaced by ancient lava flows.

Dawn will travel to the asteroid belt to carry out a detailed study of their structure and composition, shedding light on their evolution and the conditions in which these objects formed.

The mission's objectives include:

study internal structure and density

determine size, composition, shape and mass

examine surface features and craters

understand the role of water in controlling asteroid evolution

Dawn's instruments include a gamma ray and neutron spectrometer that can detect the hydrogen from water.

Evidence of whether water still exists on Ceres could come from frost or vapour on the surface. There may even be liquid water under the surface.

The water is thought to have kept Ceres cool throughout its evolution. By contrast, Vesta was hot, melted internally and became volcanic early in its development.

Frozen in time

While Ceres remains closer to the ancient state, Vesta evolved further over its first few millions of years of existence.

Dawn is expected to send back high-resolution images of these worlds, including, perhaps, mountains, canyons, craters and ancient lava flows.

VESTA

525km (326 miles) across

Surface has distinctive light and dark areas

Discovered in 1807 by Heinrich Wilhelm Olbers

Pieces of Vesta have fallen to Earth as meteorites

The instruments will help identify minerals on the surface and the elements they contain.

"[Ceres and Vesta] are revealing information that was frozen into their ancient surfaces," said Professor Russell, a professor at the University of California, Los Angeles (UCLA).

"By looking at the surface and how it was modified by the bombardment of meteoroids, we will get an idea of what the early conditions of Ceres and Vesta were and how they changed.

"So Dawn is a history trip too. We're going back in time to the early Solar System."

Dawn is scheduled to fly past Mars by April 2009, and after more than four years of travel, the spacecraft will rendezvous with Vesta in 2011.

The spacecraft will orbit Vesta for about nine months, before setting off in 2012 for a three-year cruise to Ceres.

Dawn will rendezvous with its second target in 2015, to conduct studies for at least five months.